The present invention relates to a surface treatment process for imparting hydrophilic properties to aluminum articles, such as evaporators made of aluminum and pieces of aluminum material.
Throughout the specification and appended claims, the term "aluminum" includes pure aluminum, commercial aluminum containing small amounts of impurities and aluminum alloys in which aluminum predominates, and the term "aluminum articles" refers to aluminum products and aluminum materials.
Evaporators made of aluminum for air conditioners for motor vehicles and buildings include include refrigerant tubes and fins in combination therewith. While the evaporator is in operation, the refrigerant tube and fins have a surface temperature below the dew point, permitting deposition of water droplets or drops on the surfaces of these components. The deposition of water drops provides increased resistance to the flow of air which is forced through the evaporator from one side to the other side thereof. This reduces the overall amount of air flow through the evaporator to result in a reduced heat exchange efficiency. If it is attempted to obtain the desired amount of air flow, the evaporator must be made large-sized. In recent years, however, there is the tendency that the fins are arranged at a smaller spacing to render the heat exchanger more efficient and compacter. The arrangement therefore involves greater resistance to the air flow due to the deposition of water drops. The increased resistance is attributable to the fact that the conventional aluminum product, which is untreated, has poor hydrophilic properties, such that the drops of water deposited on the refrigerant tube and fins remain in shape. In some cases, such an aluminum article is chemically treated for the purpose of giving corrosion resistance thereto. As compared with untreated articles, the aluminum article with the resulting chemical coating has improved affinity for water, permitting the deposited water drops to spread, to some extent, in the form of a film on the surface of the article to somewhat decrease the resistance to the air flow, but the problem still remains as to the reduction of the heat exchange efficiency due to the deposition of water drops.